1. Field of the Invention
The invention relates to a secondary battery temperature-increasing control apparatus and a vehicle including the same and to a secondary battery temperature-increasing control method. In particular, the invention relates to a technology for performing temperature increasing control to increase the temperature of the secondary battery with the use of the heat generation caused by the internal resistance of the secondary battery.
2. Description of the Related Art
In general, in secondary batteries, typified by lithium-ion batteries and nickel-hydrogen batteries, charging and discharging characteristics are degraded as the temperature decreases. When the temperature of the battery is low, it is required to quickly increase the temperature of the battery.
Japanese Patent Application Publication No. H11-329516 (JP-A-11-329516) describes an apparatus for increasing the temperature of a battery. In the temperature increasing apparatus, a resonance circuit is formed by connecting a series circuit consisting of an inductor, a capacitor, and an alternating-current power supply across the battery. The temperature of the battery is increased by making the alternating-current power supply generate an alternating current voltage at the resonance frequency of the resonance circuit.
In the temperature increasing apparatus, almost all the electric power is consumed in the internal resistance during resonance and the temperature of the battery is increased by self-heat generation. It is insisted that this temperature increasing apparatus is capable of effectively increasing the temperature of the battery with minimum electric power consumption (see JP-A-11-329516).
In general, it is required of secondary batteries to conform to the requirements of the upper and lower limit voltages of the batteries in view of safety and durability. However, JP-A-11-329516 merely discloses the technology for increasing the temperature of the battery and the above publication includes no discussion concerning how the temperature is efficiently increased within the range, in which the voltage does not exceed the upper limit voltage nor fall below the lower limit voltage.
The electric current generated by the resonance circuit is affected by the unevenness of the inductance L and/or the characteristics of the battery and the amount of heat generated in the battery is proportional to the square of the peak value of the electric current caused to flow by the resonance circuit. Thus, the amount of heat generated in the battery is significantly affected by the unevenness of the inductance L and/or the characteristics of the battery. The above publication, however, includes no discussion concerning any measure against such unevenness of the amount of heat generated.